The overall objective of this research component is to investigate the high-energy biochemical mechanisms whereby the perinatal brain is damaged by hypoxia-ischemia and how brain injury can be prevented or reduced through specific modalities of therapy. Specific Aims include: 1) to characterize the earliest alterations in high-energy phosphate reserves which occur during perinatal cerebral hypoxia-ischemia and to correlate these changes with perturbations in cerebral energy utilization, cerebral glucose utilization, glutamate and nitric oxide neurotoxicity, and intracellular calcium accumulation; 2) to correlate the concentrations in cerebral high-energy phosphate reserves and the changes which occur during hypoxia-ischemia using 31P magnetic resonance (MR) spectroscopic methods and enzymatic, fluorometric techniques; 3) to characterize the secondary (delayed) energy failure which occurs during recovery from perinatal cerebral hypoxia-ischemia and to correlate the alterations with the presence and severity of hypoxia-ischemic brain damage; 4) to ascertain underlying biochemical mechanisms whereby the glucocorticosteroid, dexamethasone, protects the perinatal brain from hypoxic-ischemic damage; 5) to determine the protective influence of magnesium sulfate on perinatal hypoxic-ischemic brain damage and, if so, to ascertain its mechanism of action; and 6) to investigate further the presence and extend of alterations in diffusion-weighted and T2-weighted imaging during recovery from perinatal cerebral hypoxia-ischemia and to correlate any changes with the nature and extent of cerebral edema and associated neuropathologic alterations. Seven-days postnatal rats will undergo unilateral cerebral hypoxia-ischemia, during and following which the animals will undergo those procedures necessary to obtain sequential 31P and 1H NMR spectra which will allow for measurements of the alterations in high-energy phosphate reserves and other metabolites which result from the insult. Other animals will undergo MR imaging at specific intervals following cerebral hypoxia-ischemia. Other experiments will elucidate the neuroprotective effect of dexamethasone, magnesium sulfate, and L-NAME on hypoxic-ischemic brain damage in the developing rat. Analytic procedures will include sequential measures with NMR spectroscopy as well as brain tissue analysis of high-energy phosphate reserves and other metabolites using enzymatic, fluorometric techniques.